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Cattle belonging to seven different genetic groups in Kerala state, India were chosen for the study to find out the genetic diversity between the groups, which would aid in their sustainable improvement and conservation of native cattle. They included the native groups namely, Vechur, Kasaragod, Vadakara dwarf and Vilwadri, along with three different grades of crossbred cattle, based on milk production. Genomic DNA was isolated from 20 to 30 unrelated animals of each group and a panel of 25 microsatellite markers as suggested by FAO-ISAG, were amplified by multiplex PCR. The PCR amplicons were genotyped and the allelic data analyzed using suitable Bioinformatics softwares. The present study showed that the observed number of alleles was much more than the expected, in all populations. The mean PIC value obtained for the present study was 0.8912 and increased number of private alleles were observed, especially in Vilwadri and Kasaragod groups. Negative value of F

Cluster of differentiation 14 (CD14) gene is an important molecule for innate unity and found to be significantly associated with fertility traits in cattle. The objectives of present study were to detect the single nucleotide polymorphisms (SNPs) in exon 1 region of CD14 gene and to evaluate the association of genetic variants with fertility traits viz. Service period and Age at First Calving in crossbred cattle of Kerala. The study was conducted on two hundred and sixteen crossbred cattle maintained at various farms of Kerala Veterinary and Animal Sciences University. Genomic DNA was isolated and polymorphisms of gene were detected by Single Strand Confirmation Polymorphism. Two SNPs, c.445T>G and c.432C>T were detected in exon 1 coding region of CD14 gene. The frequencies of CC and CT genotypes were 0.82 and 0.18 in the population. In addition, a significant association between SNPs and service period was observed in crossbred cattle population under study. Crossbred cattle with CT diplo types showed lower values for service period than those with CC diplo types. The association of CD14 gene with these traits emphasizes the importance of bovine CD14 as a candidate gene for marker assisted selection for fertility traits in crossbred cattle

This paper analyzes transfer trajectories from Earth to Mars with ballistic capture. To begin with, the dynamics of capture orbits on Mars is studied in the framework of a restricted three-body pro...

Potassium fluorophosphate (KFP) glasses doped with different concentrations of Dy3+ ions and co-doped with Eu3+ ions were prepared to study the luminescence spectra. Optical transition properties of Dy3+ doped KFP glasses were assessed with the aid of Judd–Ofelt (J-O) theory. Visible luminescence spectra have been obtained for Dy3+ ions and Eu3+ ions under 350 nm excitation. Yellow emission of Dy3+ was exhibited mainly due to the transition 4F9/2→6H13/2 centered at 573 nm. Energy transfer between Dy3+ and Eu3+ ions and decay curves of Dy3+ and Dy3+/Eu3+ co-doped KFP glasses have been studied using fluorescence spectra. The decay of 4F9/2 excited level is found to be single exponential for lower concentrations up to 0.3 mol% and becomes non-exponential for (greater than 0.3 mol%) higher concentrations. It is noticed that with the increase of Dy3+ concentration, the lifetime values of 4F9/2 level was decreased. Intense Reddish orange light was observed in addition to blue and yellow luminescence in these glasses. CIE chromaticity coordinates were calculated to study the generation of white light from the luminescent transitions. The results of this experiment show significant promise for use in white light applications. The effective properties of Dy3+/Eu3+ co-doped KFP glasses indicated that the present glasses might be useful for optical materials.

Toll like receptors (TLRs) are type 1 transmembrane proteins expressed in almost all cell types and activate the innate immune system. The present study involved characterization and differential transcriptional expression profiling of Toll-like receptor-2 gene in Vechur (Bos indicus) and crossbred (Bos indicus X Bos taurus) cattle of Kerala in response to anthrax vaccination. Sequence analysis revealed 2355 bp long TLR2 open reading frame encoding 784 amino acids with a signal peptide of 20 amino acid residues. The sequence of Vechur TLR2 revealed 96–99% identity with other ruminant species. At amino acid level, 94–99% similarity was observed with other livestock species. Seven nucleotide variations were observed when compared with other Indian cattle and 17 variations with Bos taurus. The five non-synonymous mutations observed in Vechur as compared to Bos indicus (GenBank Acc. No. EU413951.1 ) were p.Gln149Pro, p.Ile335Thr, p.Lys.337Arg, p.Ser345Asn and p.Met605Thr. The eight non synonymous variations observed as compared to Bos taurus (GenBank Acc. No. NM174197.2) were p.Asp63Glu, p.Gly68Ser, p.Ile111Val, p.Phe127Leu, p.His326Gln, p.Asn417Ser, p.Arg563His and p.His665Gln. This is the first report about the full-length cDNA sequence and the single nucleotide variations of TLR2 gene of the Vechur cattle, the smallest cattle of the world. The prolonged upregulation of TLR2 mRNA in Vechur cattle as compared to Crossbred cattle post anthrax vaccination is suggestive of the greater immune response of this native cattle as compared to exotic cattle.

The sealing joints used for pressure monitoring of solid propellant rocket motors (SRMs) of launch vehicles are very critical, as they are large in number, and leak through any of them is a single point failure mode. Identification of failure modes and its prevention is the key for reliable performance of an SRM. Failure modes are identified and the failure mechanisms of different seals in the pressure monitoring system studied through investigative tests with deliberately induced variations in the design parameters and nonconformance. Systematic analysis is carried out for the proposed designs through a failure mode effects analysis (FMEA), failure modes ranked in accordance with Risk Priority Number (RPN) and reliability of the joints worked out from the data. Design concerns are analyzed, alternate designs explored and innovative design solutions evolved. The effectiveness of the final design is brought out quantitatively by reduced RPN ratings and quantum jump in the reliability. Critical design, process and quality control parameters were identified, and procedures to ensure them evolved for failure mode avoidance.

Multiple gravity assist (MGA) trajectories represent a particular class of space trajectories in which a spacecraft makes use of gravity assist (GA) of one or more celestial bodies to alter its path or velocity vector, in order to reach high \(\Delta V\) targets with low propellant consumption. The search for optimal transfer trajectories can be formulated as a global optimization problem. A simple MGA problem without any deep space maneuver (DSM) considers the departure epoch and the transfer times of the trajectories between two planets as the design variables for the objective function evaluation with constraint on minimum periapsis radius at each planet. The introduction of DSM in this problem during a trajectory leg makes the model more flexible, but also more complex. Apart from the design variables taken for MGA problem, the bounds on additional variables relating to spacecraft’s relative velocity at departure planet, the time instant at which each DSM takes place, the pericenter radius at each body and the turning angle of each hyperbola are considered for the objective function assessment. This paper evaluates some benchmark MGA mission problems with one DSM. The data of these problems are available under Global Trajectory Optimization Competition (GTOC) in European Space Agency (ESA) website. These problems are optimized using the evolutionary algorithms (EAs) like differential evolution (DE), genetic algorithm (GA), particle swarm optimization (PSO), and a comparison of the results are made.

Synthetic Aperture Radar (SAR) images are widely used for a variety of applications such as surveillance, agricultural assessment and classification, planetary and celestial investigations, geology and mining, etc., due to its remarkable characteristic of capturing it under all weather conditions. SAR images are highly prone to speckle noise due to the ingrained nature of radar backscatter. Speckle removal is highly essential to limit the difficulty encountered while processing the SAR images. An exhaustive work has been done by researchers to despeckle SAR images using spatial filters, wavelet transform, and hybrid approaches. This work aims at exploring the different despeckling techniques to identify the best and suitable methodology. On measuring the despeckling performance using Peak Signal-to-Noise Ratio, Edge Preservation Ratio, Speckle Suppression Index, Speckle Suppression and Mean Preservation Index, and Structural Similarity Index simultaneously for the various techniques experimented, ridgelet transform-based thresholding works well. It gives better results by applying ridgelet transform and processing the subbands with minimax thresholding. The type and characteristics of the scene imaged also influence the result.

Trajectory estimation of a moving object using monocular visual odometry approach is an important research direction in computer vision. The moving object can be a car or a robot or anything which is carrying camera need to be tracked for autonomous navigation. Scale estimation of the translational motion is tedious in monocular visual odometry system. This paper proposes a new trajectory estimation algorithm in which Nister's 5-point algorithm is used as the baseline algorithm. We have adapted the method discussed in [1] for the scale estimation of trajectory with the additional input of camera height. Estimated scale is nothing but the ratio between the known camera height and the estimated camera height. The camera height shall be found by decomposing the Homography matrix. The proposed algorithm is tested with KITTI standard benchmark dataset [2]. Experimental results on KITTI dataset shows significant improvement in the trajectory estimation of moving object.

Synthetic Aperture Radar images have potential applications in the surveillance scenario and hence automated target detection algorithms prove to be a useful tool in monitoring and crime control as well as in marine traffic management. The advancements in marine trade have lead to the increase in the number of ships in the world waters. The usage of satellite-based radar images have become well known for maritime surveillance as ship detection is relatively simple and independent of the climatic conditions. Ships can be easily discerned in the SAR images due to their bright intensity which results due to the strong radar backscatter from their metal surface. These are the significant pixels in an image which can be gathered to detect the ship targets. During heavy sea state conditions and presence of speckle noise, sea ice and coastline structure, the ship detection process is affected since these non-ship features in the sea also exhibit high intensities in the SAR image. These false alarms have to be reduced. So, in this work a Significance based ship detection algorithm followed by a discrimination stage using ensemble classifier is proposed to differentiate the ship and non-ship targets. To enhance the ship detection process, the images are subjected to ridgelet transform based despeckling. The efficacy of the proposed Significance based target detection is proved by the obtained results.

Abort system is initiated to take the Crew Module (CM) away from the launch vehicle in case of an emergency at lift-off or at any point of time after launch for a mission with crew onboard. Crew Escape System (CES)-based abort is carried out from launch pad and during the atmospheric phase of ascent flight. The design and operation of CES play a crucial role in providing abort capability for escape from launch vehicle and return of the crew back to Earth during critical phase of ascent flight. CES motors are used to pull CM away from the launch vehicle during this mode of abort. Mission simulation and analysis is necessary for the design of CES-based abort mission and for its configuration. This article discusses the mission design, challenges faced during the design and strategies formulated towards the successful execution of Pad Abort Test.

Today's home automation technology is constantly improving flexibility by combining modern functions with the growing demands of the community. This document represents the design and implementation of a new home automation system that uses cloud computing as a service. The proposed system consists of three main components; the first part is the cloud server, which manages and manages user data and the state of information and equipment. The second part is a hardware interface module that provides the right interface for sensors and actuators that provide physical services. The third part is Home Server, which configures the hardware and provides the user interface. This document is intended to implement web services via the cloud, which in principle requires security and data availability. The proposed system is cost effective, easy and reliable and also offers a secure home automation environment for the whole family.

An algorithm is developed to find Weak Stability Boundary transfer trajectories to Moon in high fidelity force model using forward propagation. The trajectory starts from an Earth Parking Orbit (circular or elliptical). The algorithm varies the control parameters at Earth Parking Orbit and on the way to Moon to arrive at a ballistic capture trajectory at Moon. Forward propagation helps to satisfy launch vehicle’s maximum payload constraints. Using this algorithm, a number of test cases are evaluated and detailed analysis of capture orbits is presented.

In the present study, ABCG2 gene of Vechur cattle of Kerala was sequenced and aligned using Basic Local Alignment Search Tool (BLAST) in National Centre for Biotechnology Information (NCBI) site. The results revealed that ABCG2 gene sequence of Vechur cattle shows 96% similarity with reference NCBI sequences. Addition of eleven base pairs in 13th intron in ABCG2 gene of Vechur cattle which derived a larger amplicon (303 bp) than expected (292 bp). A novel SNP (G4104A) was identified at 4104th position in intron 13 of ABCG2 gene of Vechur cattle. Further research is suggested to depict the association if any of the novel SNP and unique characters of Vechur cattle.

S PACE object reentry prediction studies have been considered as one of the important topics in space research. Accurate prediction of reentry time and impact location is necessary tomitigate the Earth impact risks. There were many large objects, including the Upper Atmosphere Research Satellite, Roentgen Satellite (ROSAT), Phobos Grunt, and Gravity Field and Steady-State Ocean Circulation Satellite, which reentered Earth’s atmosphere in the recent past. It is essential to have suitablemathematicalmodels to predict the reentry time and the impact locationof riskobjects fordesigningandexecutingproper mitigation and remediation processes. Prediction of reentry time is a challenging problem because of the uncertainties in the orbital propagation models, atmospheric density models, solar flux, and geomagnetic activity indices. There are observational uncertainties in the orbital parameters as well [1]. Atmospheric drag is the major perturbing force on the spacecraft during its reentry [2]. The ballistic parameter B m∕ A × Cd (where m and A are mass and effective surface area of the object, respectively, and Cd is coefficient of drag) is a direct measure of the drag force experienced by the object. Hence, the orbital decay of the space object depends significantly on B. Orbital data of the catalogued space objects are provided by Space-Track in the form of two-line elements (TLEs). The concept of using TLE data to estimate the ballistic parameter of a reentering object has been investigated by many researchers. Chao and Platt [3] developed a lifetime prediction tool based on simplified averaged equations of motion expressed in classical orbital elements. Strizzi [4] improved Chao’s lifetime tool by using the Runge–Kutta integration technique for propagating the final orbits to reduce the uncertainty in the prediction. This improved lifetime tool was tested for its accuracy considering North American Aerospace Defense Command decayed objects [5]. Anilkumar et al. [6] used a Kalman filter approach with constant gains to estimate the ballistic parameter from TLEs. The states considered in this study were the semimajor axis, eccentricity, and ballistic parameter. The measurements were apogee and perigee altitudes computed from the TLEs. In this model, the mean U.S. standard atmosphere and a simple propagator considering atmospheric drag effects were used. Later, Sharma and Anilkumar [7] improved this method by incorporating a more accurate propagation model based on Kustaanheimo–Stiefel element equations. The constant Kalman gains were estimated byminimizing an objective function through a genetic algorithm. There are many other methodologies to compute the reentry time of a satellite using TLEs during its last orbital phase [8,9]. When the perigee altitude becomes less than a certain altitude, where the drag effect dominates the decay of the orbit, it can be termed as the last phase of orbital decay. Typically, this altitude can be taken to be 150 km. Pardini and Anselmo [10] analyzed the effect of time span (TLE data span) required to estimate the ballistic parameter of a space object by considering seven interagency space debris reentry test campaign objects. The study indicates that 10–15 TLEs provide reasonably good predictions during the final phase of reentry. An integrated model consisting of a highly accurate numerical propagation model and a multi-objective function optimization technique to estimate an essential ballistic parameter EBP k × B is presented in this paper. Here, B is the ballistic parameter and k is a factor that will absorb the uncertainties in themeasurements, models, and other inputs. In this approach, the orbital parameters are computed from TLEs using Simplified General Perturbations No.4 (SGP4) theory at their epoch and are used as the observations to predict the EBP. In this study, the high-precision orbit propagator (HPOP) utility of the Satellite Tool Kit (STK) is integrated with an optimization technique for estimating the optimal EBP. States from a pivot TLE are propagatedwith a set of ballistic parameters to generate the predictions of orbital parameters at all other TLE epochs. The innovations (observation–prediction) are then minimized to estimate the best EBP. A multi-objective function, combining the innovations on apogee and perigee altitudes, is minimized to arrive at the best EBP. Least-square errors, weighted least-square errors, considering the expected remaining life as weights, and normalized nondimensioned errors are taken as the components of the multi-objective function. In thismodel, the inaccuracies inTLEs, uncertainties inparameters likeF10.7andAp values, the inaccuracies in the atmosphericmodel, and the propagation model are all absorbed in the estimatedEBP.TheestimatedEBP isused to predict the reentry time of the object from the pivot TLE. The effectiveness of themodel is shown through the reentry time prediction ofdecayedobjects, PhobosGrunt andROSAT.This novel idea of using a multi-objective function minimization to estimate the optimal essential ballistic parameter in the reentry prediction has proven to be very effective. The present approach is different from the earlier approaches because of this novelty.

Renewable or sustainable energy sources such as photovoltaic (PV) cells usually generate variable power. The dc voltage obtained from PV system is boosted/bucked double times and used for renewable energy applications. This work proposes the design and development of a DC-DC Converter for a double buck-boost operation. This converter is suitable for low power application such as a solar water purifier system. The advantage of this converter is that instead of using two controlled switches as in case of a conventional converter, this circuit uses only one MOSFET as a switch. The circuit posses two inductors and two capacitors as energy transferring elements that are able to provide a good quality, high efficiency power supply to the load. In this paper the design of DBB converter is analyzed with closed loop control using a PI controller circuit. A simulation model of the DBB converter with results is presented. And the output of the DBB converter is given to the power supply unit of an electric water purifier and water is purified.

Large Area X-ray Propositional Counter (LAXPC) instrument on AstroSat is aimed at providing high time resolution X-ray observations in 3 to 80 keV energy band with moderate energy resolution. To achieve large collecting area, a cluster of three co-aligned identical LAXPC detectors, is used to realize an effective area in access of about 6000 cm2 at 15 keV. The large detection volume of the LAXPC detectors, filled with xenon gas at about 2 atmosphere pressure, results in detection efficiency greater than 50%, above 30 keV. In this article, we present salient features of the LAXPC detectors, their testing and characterization in the laboratory prior to launch and calibration in the orbit. Some preliminary results on timing and spectral characteristics of a few X-ray binaries and other type of sources, are briefly discussed to demonstrate that the LAXPC instrument is performing as planned in the orbit., 11 pages, 15 Figures, Accepted for publication in Journal of Astronomy and Astrophysics

An accurate estimation of the reentry time of a decaying near-Earth object is important for hazard assessment as well as for mitigation strategies. Models are important in the space scientific community to predict an accurate reentry time. In this paper three novel models namely Response Surface Method with genetic algorithm, Optimization with Satellite Tool Kit and Lifetime optimization with Satellite Tool Kit are extensively discussed. These models will predict the reentry time of decaying space objects from low-Earth-orbit (eccentricity < 0.2) through an optimization technique. Each of these models is unique in methodology and objective function. Finally the usefulness of the presented models is demonstrated by presenting reentry prediction of recently decayed space object CZ-2C rocket body. The paper compares the results obtained from these models with the observed re-entry time.

Planar fly-by trajectories from Earth to Moon are studied in the framework of restricted three-body problem (R3BP). A number of trajectories with initial conditions ( x , y , x , y ) of the form ( x 0 , 0 , 0 , y 0 ) and ( - μ , y 0 , x 0 , 0 ) close to Earth are propagated for 1000 days. The distribution of the initial conditions which will generate feasible fly-bys to Moon in the phase space are plotted in Jacobi constant, C verses initial x or y plots with color codes on time of flight. It is observed that the flyby trajectories with similar flight duration appear in clusters and show some distinctive patterns. For example for the initial condition of first type the fly-by trajectories with flight duration of about 14 to 16 days appear as a curve in the phase space. While for the second type of initial conditions the trajectories with flight duration ⩽5 days and 5–15 days appear as a band on the phase space. Poincare surface of section technique is used to identify the existence of periodic and quasi-periodic orbits in other regions of the phase space.

Lifetime estimation of space objects is very important for space debris related studies including mitigation studies and manoeuvre designs. It is essential to have a fast and accurate lifetime prediction tool for studies related to long term evolution of space debris environment. This paper presents the details of the Orbit Prediction using Semi-Analytic Theory (OPSAT) used for lifetime estimation of space objects. It uses BFGS Quasi-Newton algorithm to minimize least square error on apogee and perigee altitudes of a given TLE set to estimate ballistic coefficient (BC). This BC is used for future orbit prediction. OPSAT is evaluated for long term and short term orbit prediction using TLE data. It has been used for identification of potential candidate for active debris removal (ADR) and future projection of space debris environment with ADR.

Due to increase in the satelite launch activities from many countries around the world the orbital debris issue has become a major concern for the space agencies to plan a collision-free orbit design. The risk of collisions is calculated using the in situ measurements and available models. Spatial density models are useful in understanding the long-term likelihood of a collision in a particular region of space and also helpful in pre-launch orbit planning. In this paper, we present a method of estimating model parameters such as number of peaks and peak locations of spatial density model using continuous wavelets. The proposed methodology was experimented with two line element data and the results are presented.

In order to design a WSB trajectory to Moon, highly elliptical geocentric orbit is propagated forward in time so that its perigee increases to Earth-Moon distance. Another highly elliptical selenocentric orbit is propagated backward in time till it starts moving towards Earth. The two trajectories are patched using Fixed Time of Arrival targeting method to obtain a WSB transfer trajectory. In this paper, various geocentric and selenocentric orbits are considered and eligible candidates for WSB transfer are represented on the phase space with color code on transfer time. Genetic Algorithm is used to find patching points to reduce the sum of $\Delta V$ required at the patching points. Lunar fly-by on the way to apogee is also studied.

The present study was envisaged to conduct a quantitative analysis of various ecosystems of Attappady, Kerala to document plant diversity and structural parameters. Floristic composition and structural features of evergreen forest revealed that the occurrence of a total 42 species belonged to 25 families. Euphorbiaceae represented maximum genera of 6 species. Importance value index recorded maximum for Cullenia exarillata, which is the most dominant species of this evergreen community. This forest is identified as the only natural habitat from which Vateria macrocarpa, the rare endemic tree of Western Ghat is recorded. Structural analysis of moist deciduous forest revealed that a total 36 species belonging to 24 families. Wrightia tinctoria was the most dominant species in this community, as it constituted highest IVI. Other dominant species in this community were Terminalia bellirica and Grewia tiliifolia. Taxonomic inventory of dry deciduous forest revealed that occurrence of a total 27 tree species belonging to 18 families. Euphorbiaceae represented maximum genera of 4 species. Structural analysis showed that though the density was reported maximum for Albizia amara, the species with highest basal area (Givotia moluccana) represented the maximum importance value index. The canopy levels of the forests were relatively few with predominance of Albizia amara and Cassine albens. Plant diversity of these forest ecosystems indicted that the evergreen forest had highest diversity as indicated by maximum value for Shannon Weiner index and Simpson’s index followed by moist deciduous forest. Dry deciduous forest registered lowest values for all diversity indices.

A stochastic prediction model for the sunspot cycle is proposed. The prediction model is based on a modified binary mixture of Laplace distribution functions and a moving-average model over the estimated model parameters. A six-parameter modified binary mixture of Laplace distribution functions is used for the modeling of the shape of a generic sunspot cycle. The model parameters are estimated for 23 sunspot cycles independently, and the primary prediction-model parameters are derived from these estimated model parameters using a moving-average stochastic model. A correction factor (hump factor) is introduced to make an initial prediction. The hump factor is computed for a given sunspot cycle as the ratio of the model estimated after the completion of a sunspot cycle (post-facto model) and the prediction of the moving-average model. The hump factors can be applied one at a time over the moving-average prediction model to get a final prediction of a sunspot cycle. The present model is used to predict the characteristics of Sunspot Cycle 24. The methodology is validated using the previous Sunspot Cycles 21, 22, and 23, which shows the adequacy and the applicability of the prediction model. The statistics of the variations of sunspot numbers at high solar activity are used to provide the lower and upper bound for the predictions using the present model.

The events that occurred after 2007 such as Chinese anti-satellite test, explosion of Briz-M upper stage, break up of cosmos-2421 and collision of cosmos-2251 with Iridium-33 satellites have completely changed the spatial density patterns in low earth orbits. This has increased the risk of collision between active satellites and debris created by them. Aftermath, the risk assessment of possible collisions called as conjunction analysis of working satellites from day to day has become more crucial. Spatial density models are useful in understanding the long-term likelihood of a collision in a particular region of space and helpful in pre-launch orbit planning. In this paper we present an algorithmic procedure for automatically estimating exact model parameters corresponding to the peak location and number of peaks using wavelets that will speed up the parameter estimation process for the models with peaks.

Hydraulic servo actuators are employed for the thrust vector control of the liquid engines. Vane type gas motor, the prime mover of the system, is a critical subsystem with intricate dynamic elements such as rotor, bearings, vanes and speed regulator. Failure prevention of such critical systems, which is of paramount importance to the success of a launch vehicle mission, depends on making the design robust and ensuring that the critical parameters of the system hardware are within the specified range to give optimal performance. This paper addresses the strategies for achieving the design robustness through severe environmental stress testing and realisation of system hardware complying with quality requirements, which are essential for failure prevention. Towards this, critical environments for the gas motor have been identified and testing extended much beyond the system qualification levels, inducing failures. The test observations and data are analysed critically and design modifications made for broadening the operating environments. The quality systems and procedures for the system hardware are strengthened to assure reliable performance of the gas motor.

Analysis of the time series data collected from a stationary location in the continental shelf of the southeastern Arabian Sea during different month indicated prominent internal wave (IW) activity. Time evolution of temperature, resolved using Morlet wavelet technique, revealed that maximum energy was concentrated in the diurnal band at the density interface, whereas within the interior of thermocline, the dominant energy concentration shifted to semi-diurnal band. Both these harmonics have maximum amplitude (>15 m) during the pre-monsoon and monsoon season when the water column was highly stratified (>0.05 kg/m4), but they were not discernable in the temperature record when the stratification was weak (i.e., especially during winter). An acoustic propagation model based on ray theory, Bellhop (http:/oalib.hlsresearch.com/modes/acoustictoolbox/at.zip) was utilized to compute the transmission loss (TL) associated with the passage of low-frequency IWs. The TL was computed using the model considering (1) range-dependent and range-independent environmental scenario and (2) for different source and receiver depth configurations. Intermittent fading of acoustic signals was observed in the presence of IW. It was also observed that fading of signals very much depends on the source–receiver configuration.

Time series of temperature and salinity collected from a station in the NE Arabian Sea during March, April, May, October, and November was utilized to explain the behavior of internal tides. Analysis revealed the existence of semi-diurnal internal tides and high frequency (HF) internal waves (IW). It was observed that the amplitudes of HF IWs were determined by the degree of stratification in the thermocline. Corresponding to an increase in the density gradient in thermocline (0.016 kg/m4 in April to 0.14 kg/m4 in October), the temperature fluctuations due to internal tides increased from 1.5°C, respectively. Brunt-Vaiisala frequency also showed similar variations (∼10 cph to 22 cph). Within the thermocline, semi-diurnal internal tides caused fluctuations of >10m in the isotherm depths. A linear regression equation was fitted to parameterize the amplitude of HF IWs and its upper frequency limit in terms of thermocline gradient. The IW and one-dimensional models simulated the presence of interna...

Thenumber of space debris objects in the low Earth orbits,especially in the sun synchronous orbits,is increasing, and the breakups in 2007 have added more risk to the satellites in this region. It is necessary to study the risk of conjunctions in these orbits to plan a future course of action regarding the control and mitigation of space debris objects. A statistical approach to obtain the number of conjunctions in a prescribed altitude bin considering various inclinationbandsispresentedinthispaper.ThelowEarthorbits,whichareaffectedthemostbytheaccumulationof space debris objects, are analyzed with special emphasis on sun synchronous orbits. The study is based on the cataloguedobjectsfromthetwolineelementsets.Itisobservedthat,afterthemajorbreakupsin2007,thenumberof conjunctionsinthesunsynchronousorbitalregionishighlysignificant.Thesecondpartofthestudyconcentrateson themodelingaspectsofspatialdensityandbringsoutastochasticmodelbasedonamixtureofLaplacedistributions. ItisnotedfromthemodelthatthefragmentationeventsinlowEarthorbitduring2007haveredefinedthepatternof spatial density distribution in the region below 1100 km. Nomenclature a = area parameter in the modified Laplace distribution di = half-range of the inclination band under consideration, deg